Subject invention relates generally to engines, or prime movers, and more particularly to engines utilizing expanding fluids or gasses as the power-producing medium, or working fluid, such as gasoline engines or steam engines.
Historically engines of the expanding fluid type suffer from difficulties in lubrication between the piston and cylinder walls. Oil sumps are used and splash or pressure systems carry the oil from the sump to the cylinder walls in the path of the advancing piston. This oil bath of the cylinder walls serves both to carry heat away from the cylinder and to lubricate. Then special oil rings, or oil "wipers" are placed on the piston to scrape away excess oil and thus attempt to keep oil from gaining admission to the cylinder area on the "power" side of the piston. Then "compression" rings are placed on the piston in an attempt to prevent leakage of the working fluid past the cylinder walls and into the oil sump, and for other reasons. It follows, then, that special and expensive materials, machining, etc., are employed to effect these requirements and the tolerances that must be held are very close.
Furthermore, in low-temperature engines of today utilizing the expansion properties of fluids which have a "low-temperature" boiling point, or using gasses at the optimum portion of the temperature/expansion or pressure/expansion curves, considered "low-temperature" devices in relation to the usual operating temperatures of the so-called "gasoline" engines, the fluids or gasses utilized are frequently solvents of greases oils, thus adding to the difficulties by the possibility of "freezing" or siezing of the piston within the cylinder walls.
Moreover, in the case of the steam engine, for example, steam, water and oil may mix together, thus requiring special and expensive articles of equipment such as oil seperators, dehydrators, etc., in an attempt to keep the overall system from being contaminated by, in areas where they apply, oil, steam, water, etc.